The invention relates to new and useful improvements to commutator motors. More particularly, the invention relates to arrangements for deflecting moving charge carriers in a brush for the commutator motor.
In a commutator motor, the operating current is normally supplied to the rotor winding via a first brush contacting the commutator, and is extracted again via a second brush, which is circumferentially offset on the commutator with respect to the first brush. The brushes are held either in so-called hammer brushholders or in so-called box brushholders. Their sliding surfaces are pressed, generally by means of spring pressure, against the surfaces of the laminates of the commutator and, as a result, are subject to wear. Some of this wear is caused by so-called brush sparking on the trailing edge of the brushes. This brush wear shortens the life of the brush system and adversely affects the motor operating characteristics.
British Patent Specification GB-A-167 159 is intended to avoid brush sparking in a commutator motor by deliberately keeping away from the brushes any stray flux between the stator winding at one axial end of the commutator, on the one hand, and a stator magnetic return path at the other axial end of the commutator, on the other hand, by means of separate flux guides which surround the brushholder and the brushes on the outside.
British Patent Specification GB-B 55 10 describes how undesirable brush sparking on the trailing edge can be counteracted by multilayer brushes, which have a higher electrical resistance brush located at a leaving edge of a brush that has a lower electrical resistance.
German Utility Model DE 91 06 977 U1 describes a commutator motor, particularly for driving motor vehicle accessories, in which, in order to prevent interference caused by brush noise, the brushes are split along a separating line (which runs essentially parallel to the direction of the operating current and the contact-pressure direction) into two sub-zone brushes. These two sub-zone brushes differ in material composition from one another, in such a manner that the sub-zone including the leading edge has a higher proportion of copper than the other sub-zone, that includes the trailing edge. Complex special manufacturing techniques are required to produce such two-zone brushes.